# This example has a couple of roles:
# 1.  I use generalizations of it in real work.  A sample
#     usage is
#         source other_tcl
#         
#         set a 13
#         set b 79
#         
#         puts [perl_interpret {
#             $result = [set a] + [set b];
#             print "The sum is ", $result, ".\n";
#         }]
#     Roughly, anything within the {} can be normal Perl code, except that
#     unescaped []-s are available for Tcl-side command substitution.
#
#     In practice, I usually have slightly more involved proc definitions,
#     which implement various kinds of introspection, logging, invocation
#     of processors other than Perl, improved exception-handling, ...
#
#     Reasons to use other languages:  Perl's REs, Python's mathematics
#     extension, ...
# 2.  It's a minimal example of significant use of uplevel and subst.
#     [Sometime I should show RE uses of subst, and the do-while I've
#     published somewhere.]

proc perl_interpret script {
  return [exec perl << [uplevel [list subst -novariables -noback $script]]]
}